The present invention relates to radio paging systems and more particularly to a highly reliable radio paging system.
A variety of different types of radio paging systems are in widespread use. For example a radio paging system that uses a variation of the well known POCSAG protocol is shown in U.S. Pat. No. 4,398,192 (Moore) and a system that broadcast messages using an FM subcarrier is shown in U.S. Pat. No. 4,713,808 (Gaskill). None of the known systems is absolutely reliable, that is, none of the known systems can guarantee that one hundred percent of the messages transmitted will be received by the intended receiver. Problems associated with message reception reliability are accentuated when the size of the receivers is decreased. For example the wristwatch like receiver shown in U.S. Pat. No. 4,713,808 (Gaskill) imposes severe restrictions on battery size and on the antenna, thereby creating sensitivity or message completion reliability problems.
The present invention provides a highly reliable radio paging system. The radio paging system of the present invention provides a combination of time, frequency and spacial diversity in order to increase the reliability of the system. Time diversity is provided by broadcasting the same message at a number of different times. Spacial diversity is achieved by broadcasting the same message from a number of different locations. Frequency diversity is achieved by broadcasting the same message at a number of different frequencies. The paging receiver according to the present invention is designed to receive messages on a number of different frequencies; however, the pager only responds to a message the first time that it receives the particular message. The combination of time, frequency, and spacial diversity provided by the present invention results in a highly reliable radio paging system.